Silver halide photographic material

ABSTRACT

The present invention provides a photographic material comprising on a support (i) photosensitive silver halide particles, (ii) substantially light insensitive silver salt particles having a speed at least a factor 10 less than said photosensitive silver halide particles under the same conditions of exposure and development of said photosensitive silver halide particles and (iii) a releasing compound capable of image-wise releasing under the conditions for image-wise development of said photosensitive silver halide to silver a chemical sensitizer, said chemical sensitizer rendering said substantially light insensitive silver salt particles developable. The present invention also provides a method for making an image therewith and a method for making a lithographic printing plate.

DESCRIPTION

1. Field of the Invention

The present invention relates to a photographic material and a methodfor producing images therewith.

2. Background of the Invention

In the art of silver halide photography it is well known to usecompounds that image-wise release a photographic useful group such ase.g. a dye or dye precursor, a silver halide solvent, a fogging agent,an anti-fogging agent, a development inhibitor, a developmentaccelerator, a developing agent, a chemical or spectral sensitizingagent, a toning agent etc.. Some of these type of compounds are commonlyemployed to produce colour images (see for example Angew. Chem. Int. Ed.Engl. 22 pages 191-209, 1983) but are also useful in black and whitematerials to obtain a photographic material having a high speed, highcontrast etc.. For example U.S. Pat. No. 4,724,199 discloses compoundscapable of releasing a fogging agent to obtain a photographic materialof high speed and high contrast.

Some of these type of compounds may also be used to obtain a negativeworking silver salt diffusion transfer material. See for example U.S.Pat. No. 4,693,955 and the Japanese published unexamined patentapplication no. 15247/59. By the term "negative working" is meant thatthe exposed parts of the photographic material yield the image partswhile the term "positive working" implies the formation of image partscorresponding to the non-exposed parts of the photographic material.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a new type ofphotographic material of high speed and good contrast.

It is a further object of the present invention to provide a method forobtaining an image with said photographic material.

It is a third object of the present invention to provide a method formaking a negative or positive working lithographic printing plate basedon the silver salt diffusion transfer process using said photographicmaterial.

Further objects will become clear from the description hereinafter.

According to the present invention there is provided a photographicmaterial comprising on a support photosensitive silver halide particles,and substantially light insensitive silver salt particles having a speedat least a factor 10 less under the same conditions of exposure anddevelopment of said photosensitive silver halide particles than saidphotosensitive silver halide particles and a releasing compound capableof image-wise releasing under conditions for image-wise developing saidphotosensitive silver halide particles to silver a chemical sensitizersaid chemical sensitizer rendering said substantially light insensitivesilver salt particles developable.

According to the present invention there is also provided a method formaking an image using the photographic material defined above..

According to the present invention there is also provided a method formaking a negative or positive working lithographic printing plate usingthe photographic material defined above.

DETAILED DESCRIPTION OF THE INVENTION

In the method of the present invention during the development step achemical sensitizer rendering the substantially light insensitive silversalt particles developable is released either mainly in the exposed ormainly in the non-exposed areas.

According to a first embodiment of the present invention compounds thatpreferably release the chemical sensitizer in their reduced state can beincorporated in the photographic material in their reduced state. Thusfor a negative working photosensitive silver halide emulsion duringdevelopment the developing agent will be oxidized in the exposed areasand will be able to oxidize tile releasing compound in the exposedareas. In the non-exposed areas the developing agent will remain in itsreduced state thus not being able to oxidize the releasing compound.Since the reduced form of the releasing compound according to this firstembodiment preferably releases the chemical sensitizer under theconditions of development of the photosensitive silver halide thechemical sensitizer will be mainly released in the non-exposed areasthus rendering the substantially light insensitive silver salt particlesdevelopable in the non-exposed areas. Therefore in the exposed areasonly the photosensitive silver halide will be developed while in thenon-exposed areas the substantially light insensitive silver saltparticles will be developed and probably also the photosensitive silverhalide. Since the combination of the photosensitive silver halide andsubstantially light insensitive silver salt can be choosen such thatmainly the substantially light insensitive silver salt contributes tobuilding up of density e.g. by using more light insensitive silver saltthan photosensitive silver halide or by using a coarse grainphotosensitive silver halide and a fine grain light insensitive silversalt the density in the exposed parts will be less than in thenon-exposed parts.

According to a second embodiment the releasing compound can beincorporated in its oxidized state and mainly the reduced form of thereleasing compound is capable of releasing the chemical sensitizer.During development of a negative working photosensitive silver halideemulsion the developing agent will be consumed in the exposed areas dueto development of the exposed silver halide and as a consequence thereleasing compound mainly remains in its oxidized state in the exposedareas. In the non-exposed areas the releasing compound will be reducedby the developing agent so that the release of the chemical sensitizerin the non-exposed areas will be enabled under the conditions ofdevelopment. As a consequence the chemical sensitizer will be mainlyreleased in the non-exposed areas where it renders the substantiallylight insensitive silver salt particles developable. Similar asexplained in the first embodiment this will result in a larger densityin the non-exposed parts than in the exposed parts.

According to a third embodiment of the present invention a releasingcompound capable of preferably releasing in its oxidized form thechemical sensitizer is incorporated in the oxidized state. Duringdevelopment the developing agent will be consumed in the exposed areasof a negative working photosensitive silver halide emulsion due todevelopment of the exposed silver halide so that the releasing compoundremains in the oxidized state in the exposed areas and will be reducedin the non-exposed areas by the developing agent. As a consequence thechemical sensitizer will be mainly released in the exposed areas wherethe chemical sensitizer will render the light insensitive silver saltparticles developable. In this embodiment none or practically none ofthe silver halide and silver salt in the non-exposed areas will bedeveloped while both the photosensitive silver halide and substantiallylight insensitive silver salt in the exposed areas will be developed.This embodiment and the subsequent fourth and fifth embodiment thatoperate in a similar way offer the advantage over a silver halidematerial containing no releasing compound and substantially lightinsensitive silver salt that high speed photosensitive materials can beobtained without loss of image quality especially the image density.

According to a fourth embodiment of the present invention a releasingcompound capable of preferably releasing in its oxidized form thechemical sensitizer is incorporated in tile reduced state. Duringdevelopment the developing agent will be oxidized in the exposed areasof a negative working photosensitive silver halide emulsion due todevelopment of the exposed silver halide so that the oxidized form ofthe developing agent will be capable of oxidizing the releasing compoundto its oxidized state in these areas while the releasing compound willremain in its reduced state in the non-exposed areas. As a consequencethe chemical sensitizer will be mainly released in the exposed areaswhere the chemical sensitizer will render the light insensitive silversalt particles developable..

According to a fifth embodiment of the present invention releasingcompounds can be used that release the chemical sensitizer compound upona coupling reaction with the oxidized form of the developing agent torelease the chemical sensitizer. During development the developing agentwill be oxidized in the exposed parts of a negative workingphotosensitive silver halide emulsion so that in these areas a couplingreaction of the oxidized form of a developing agent with the releasingcompound to release the chemical sensitizer can take place. As aconsequence the substantially light insensitive silver salt particleswill be rendered developable in the exposed parts of the photographicmaterial.

According to a sixth embodiment of the present invention a releasingcompound can be used that releases the chemical sensitizer under thedeveloping conditions upon reaction with silver ions. Since the silverions are developed to silver in the exposed parts of a negative workingphotosensitive silver halide emulsion the reaction will mainly takeplace in the non-exposed areas of the photosensitive silver halideemulsion so that the sensitizer will be released in tile non-exposedareas.

Depending upon the type of releasing compound and the releasingmechanism it is thus possible to manufacture a negative or positiveworking photographic material comprising a negative workingphotosensitive silver halide emulsion. It is further clear to a personskilled in the art that when a positive working photosensitive silverhalide emulsion is used the release of the chemical sensitizer will takeplace in areas opposite in image value with regard to the areas whererelease takes place in the negative working emulsions.

Releasing compounds suitable for use in accordance with the presentinvention correspond to general formula (A) or (B):

    CAR--(TIME).sub.n --Q                                      (A)

wherein CAR represents a carrier moiety that upon reaction with eitherthe reduced or oxidized form of a developing agent or upon reaction withsilver ions is capable of releasing under the conditions for developmentof the photosensitive silver halide the moiety --(TIME)_(n) --Q, TIMErepresents a so called timing group which releases Q subsequent to therelease of --(TIME)_(n) --Q from CAR, Q represents a chemical sensitizercapable of rendering silver salt particles developable and n represents0 or 1; ##STR1## wherein CAR has the same meaning as defined above, xrepresents an integer from 2 to 20, Y represents S, Se or Te and Zrepresents the necessary atoms to form together with Y_(x) and CAR aring.

A variety of reactions for releasing a compound under silver halidedeveloping conditions from a carrier moiety are known in the prior art.Such reactions for releasing and carrier moieties suitable for use inaccordance with the present invention are disclosed in e.g. "Dyediffusion systems in colour photography" Angew. Chem. Int. Ed. Engl.1983 volume 22 pages 191-209 and references cited therein, U.S. Pat. No.4,916,047, Japanese published unexamined patent applications no.271345/63 and 287857/63, EP 198,438 and EP 347,849.

Preferably used releasing reactions are e.g. a redox reaction of thedeveloping agent with the carrier moiety or a coupling reaction of theoxidized form of the developing agent with the carrier moiety.

Preferably used carrier moieties for use in a redox reaction with thedeveloping agent are shown in table 1.

                  TABLE 1                                                         ______________________________________                                        Carriers for use in a redox                                                   reaction with the developing agent.                                           ______________________________________                                         ##STR2##                                                                      ##STR3##                                                                      ##STR4##                                                                      ##STR5##                                                                      ##STR6##                                                                      ##STR7##                                                                      ##STR8##                                                                      ##STR9##                                                                      ##STR10##                                                                     ##STR11##                                                                    ______________________________________                                    

In the above formulas each of R¹, R², R³ independently represents analkyl group, an arylalkyl group, an alkylaryl group or an aryl groupeach of which may be substituted, an alkyloxy or a halogen atom, R¹ andR² may be linked to each other to form a ring, R⁴ has one of thesignificances given for R¹ or represents hydrogen, Ball represents aballast group well known in the art e.g. the ballast groups disclosed inU.S. Pat. No. 3,358,700, 4,266,019, 4,232,312, 4,513,082, 3,894,895,3,664,841, Z represents O or S and EAG represents an electron acceptinggroup e.g. those disclosed in U.S. Pat. No. 4,916,047, Japanesepublished unexamined patent applications no. 271345/63 and 287857/63.

Preferred carrier moieties for use in a coupling reaction with theoxidized form of a developing agent are e.g. acylacetamides such asbenzoylacetanilides and pivalylacetanilides, cyclic carbonyl containingcompounds, pyrazolones, pyrazolotriazoles, phenols and naphtols etc..Specific examples are shown in table 2.

                  TABLE 2                                                         ______________________________________                                        Carriers for release upon a coupling reaction                                 with the oxidized form of a developing agent.                                 ______________________________________                                         ##STR12##                                                                     ##STR13##                                                                     ##STR14##                                                                     ##STR15##                                                                     ##STR16##                                                                     ##STR17##                                                                     ##STR18##                                                                     ##STR19##                                                                    ______________________________________                                    

In the above formulas each of R⁵ and R⁷ independently represents ahydrogen, a ballast group, an alkyl, arylgroup or alkoxy group each ofwhich may be substituted and R⁶ represents one or more substituentsselected from halogen, an alkyl or alkoxy having 1 to 4 carbon atoms.

Suitable timing groups for use in accordance with the present inventionare disclosed in e.g. EP 403019 and EP 347849. Specific examples oftiming groups are shown in table 3.

                  TABLE 3                                                         ______________________________________                                         ##STR20##                                                                     ##STR21##                                                                     ##STR22##                                                                     ##STR23##                                                                    ______________________________________                                    

Examples of moieties Q capable of rendering a silver salt emulsiondevelopable after release from the carrier moiety for use in accordancewith the present invention are shown in table 4. Further moieties Qsuitable for use in accordance with the present invention are disclosedin e.g. U.S. Pat. No. 4,518,682.

Table 4

    --Y.sub.x --(TIME).sub.t --CAR'

wherein x and Y have the same meaning as defined above, t may be 0 or 1and CAR' has one of the significance given for CAR defined above and maybe the same as CAR but may also differ from CAR provided that both CARand CAR' react in the same manner

    --Y.sub.x --R.sup.8

wherein x and Y have the same meaning as defined above and R⁸ representsan alkyl, an aryl, an alkylaryl or acyl group each of which may besubstituted,

    --S--SO.sub.2 --R.sup.8

wherein R⁸ has the same meaning as defined above ##STR24## wherein eachof R⁹ and R¹⁰ independently represent hydrogen, an alkyl or aryl or acylgroup that may be substituted, L represents a divalent linking groupe.g. --SO--, --SO₂, --S--, --O--, --CO--, an ester, an amide, an amine,a carbonate, an alkylene, an alkenylene, an arylene etc. ##STR25##wherein L, R⁹ and R¹⁰ have the same meaning as defined above

Examples of compounds corresponding to general formula (A) or (B) areshown in table 5. Other compounds suitable for use in accordance withthe present invention are disclosed in e.g. U.S. Pat. No. 4,518,682.

                                      TABLE 5                                     __________________________________________________________________________    compounds corresponding to formula (A)                                        __________________________________________________________________________     ##STR26##                                                   1A                ##STR27##                                                   2A                ##STR28##                                                   3A                ##STR29##                                                   4A                ##STR30##                                                   5A                ##STR31##                                                   6A                ##STR32##                                                   7A                ##STR33##                                                   8A                ##STR34##                                                   9A                ##STR35##                  10A                                                                               ##STR36##                   11A                ##STR37##                  12A                                                                               ##STR38##                   13A                ##STR39##                                                  14A                ##STR40##                                                  15A                ##STR41##                                                  16A                ##STR42##                                                  17A                ##STR43##                                                  18A                ##STR44##                                                  19A                ##STR45##                                                  20A                ##STR46##                                                  21A               Examples of formula (II)                                                       ##STR47##                  IB                                                                                ##STR48##                   2B                 ##STR49##                  3B                                                                                ##STR50##                   4B                 ##STR51##                                                  5B                __________________________________________________________________________

Compounds 1A to 3A can be prepared according to the following scheme(I): ##STR52## wherein R¹, R², R³, R⁴ and R⁹ have the same meaning asdefined above.

The procedure according to scheme (I) is exemplified by the followingpreparation of compound 2A (R¹ and R² together forming a cyclohexane, R³being --C₆ H₅ --O--C₁₆ H₃₃, R⁴ and R⁹ being CH₃).

Preparation of Compound (IB)

To a solution of 37.5g of m-aminoacetanilide in 375 ml of pyridine wasadded 186 g of compound (IA) (for the preparation of (IA) see e.g.EP-A-173361). The suspension was stirred for two hours at 50° C. Thenthe reaction was poured on 3.5 l of a hydrogen chloride solution (2N)which was ice cooled. The resulting precipitate was dissolved in 1.2 lof toluene and extracted with 500 ml of a 1N solution of hydrogenchloride and subsequently with 500 ml of water, The product wascrystallised from 1.51 of hexane. (yield: 204 g; melting point: 221° C.)

Preparation of Compound (IC)

To a solution of 42.9g of compound (IB) in 600 ml of1-methoxy-propan-2-ol and 60 ml of water was added 120 ml of HCl (12N).The solution was refluxed for 30 min. and subsequently cooled to 50° C.The mixture was then carefully poured on a solution of 150 g of NaHCO₃in 21 of water. The precipitate formed was filtered and dried. Theproduct was chromatographically purified (SiO₂, eluent:dichloromethane/methanol 95:5). (yield: 11.5 g; melting point: 81.9° C.)

Preparation of Compound 2A

To a solution of 4.1 g of compound (IC) in 5 ml of acetonitrile wasadded 1.82 g of methylisothiocyanate. The reaction was stirred for 7days at room temperature. The solvent was evaporated and the product waschromatographically purified (SiO₂, eluent: dichloromethane/ethylacetate85:15). (yield: 2.5 g; melting point 101.2° C.).

Compound 4A can be prepared according to the following scheme (II):##STR53##

Compound 5A can be prepared according to a similar procedure. Thepreparation of compound 4A according to scheme (II) is as follows:

Preparation of Compound (IIB)

A solution of 35.8 g of compound (IIA) in 150 g of ethylenediamine wasstirred for 5 hours at room temperature. The solution was then poured ina mixture of ice-water and acetic acid. The precipitate which formed wasfiltered and washed with water and finally dried.

Preparation of Compound 4A

A solution of 7.3 g of compound (IIB) and 1.1 g of methylisothiocyanatein 50 ml of tetrahydrofuran is refluxed for 1 hour and subsequentlycooled and poured in water. The precipitate which formed was filteredand recrystallised from 2-methoxyisopropanol.

Compound 6A can be prepared as follows:

2.9 g of 2-stearylamido-4-(p-amino-benzenesulfonamido)-naphthol wasbrought in 48 ml of toluene and 8 ml of the mixture was removed byazeotropic destillation. The mixture was then cooled to 80° C. and 0.43g of Si(NCS)₄ was added. The mixture was stirred for 1 hour at 80° C.and a same amount of Si(NCS)₄ was subsequently added. The mixture wasthen stirred for another 2 hours at 80° C. and left to stand overnight.The solvent was then removed and the remaining residue redissolved in amixture of 9Oral of isopropanol and 10 ml of water. This solution wassubsequently filtered to remove the SiO₂ which formed during thereaction. The solvent of the filtrate was removed and compound 6A wasobtained as a yellow powder.

Compound 7A can be prepared according as follows:

134.7 g of 2-(4-stearyloxyphenyl)-3-amino-indole and 85 g ofp-chlorosulfonylacetanilide were brought in 11 of aceton. Whilststirring 49 ml of pyridine were added and the mixture was subsequentlyrefluxed for 8 hours. The obtained reaction mixture was cooled andpoured in an 1 mol/l aqueous solution of HCl. A precipitate was obtainedwhich was filtrated, washed and dried. 190 g of the obtained precipitatewas dissolved in 1.31 of ethanol and 125 ml of an aqueous HCl solution(7.5mol/l) were dropwise added during a period of 20 min.. The obtainedmixture was refluxed for 8 hours and subsequently cooled to 35° C. Aprecipitate was formed which was filtrated and washed with 100 ml ofethanol. The precipitate was then stirred in a mixture of 11 ofethylacetate 35 ml of 25% aqueous NH₄ OH solution and 500 ml of water.The ethylacetate layer was then separated and the ethylacetate solventwas subsequently removed under reduced pressure.

A solution of 15.1 g of the thus obtained residue and 7.32 g ofmethylisothiocyanate in tetrahydrofuran was stirred for 10 days at roomtemperature. Compound 7A was obtained as a precipitate andrecrystallized from acetonitrile. The melting point was 143° C.

Compound 8A was prepared as follows:

Preparation of α-pivaloyl, α-(4-nitrophenoxy)-(4-carbethoxy)acetanilide.A solution of 21.9 g of p-nitro-phenol and 37.5 ml of tetramethylguanidine in 250 ml of acetonitrile was added to a solution of 48.8 g ofα-chloor, α-pivaloyl(4-carbethoxy)acetanilide and the resulting mixturewas stirred for 3 hours at 40° C. The reaction mixture was thenneutralized with 30 ml of HCl (5N) en diluted with 250 ml of water. Aprecipitate formed which was separated and recrystallized fromacetonitrile.

Preparation of α-pivaloyl, α-(4-aminophenoxy)-(4-carbethoxy)acetanilide.In 128 ml of 2-methoxyisopropanol were dissolved 12.85 g of α-pivaloyl,α-(4-nitrophenoxy)-(4-carbethoxy)acetanilide, 3.82 g of piperidine and0.3 ml of a Raney Nickel suspension. To this solution was guidedhydrogen gas at a pressure of 3 bar during 3 hours. The solids in themixture were removed and the solution was evaporated. The yellow oilobtained was dissolved in dichloromethane, washed with water and thedichloromethane was subsequently removed under reduced pressure. Theresulting oil was crystallized in toluene.

Preparation of Compound 8A

A solution of 9.95 g of α-pivaloyl,α-(4-aminophenoxy)-(4-carbethoxy)acetanilide and 2.8 g ofmethylisothiocyanate in 75 ml of tetrahydrofuran was refluxed for 2hours. To the mixture was then added 275 ml of n-hexane whilst stirring.An oil formed and the liquid was decanted. The oil was further stirredwith hexane until it solidified.

Compound 9A was prepared in a similar way as compound 8A.

Compounds 14A to 18A can be prepared according to the following scheme(III): ##STR54##

R¹, R², R³ and R⁴ have the same meaning as defined above. If anassymmetric molecule is to be prepared a mixture of compounds (IIID) isused in step (4) of scheme (III). Compounds 10A to 13A may also preparedaccording to a variation of scheme (III) i.e. by reacting compounds offormula (IIID) in scheme (III) with compounds corresponding to R⁸ --SSO₃⁻ Na⁺ wherein R⁸ has the same meaning as defined above.

The procedure for preparing compounds 14A to 18A according to scheme(III) is examplified for compound 14A of table 5 (R¹ and R² togetherforming a cyclohexane, R³ being --C₆ H₅ --O--C₁₆ H₃₃ and R⁴ being CH₃)by the following procedure:

Preparation of Compound (IIIB) of Scheme (III)

To 52.4 g of compound (IIIA) (for preparation of (IIIA) see EP-A-109701)dissolved in 600 ml of ethyl acetate was added in portions 87 g ofmanganese dioxide. The suspension was reacted at reflux temperature for1 hour. Next, the solid was filtered, and the filtrate was partlyconcentrated. Compound (IIIB) precipitated on cooling. The product wasfiltered and washed with cold ethyl acetate. The yield was 44 g (84%)and the melting point was 87%.

Preparation of Compound (IIIC) of Scheme (III)

To 25.6 g of compound (IIIB) dissolved in 1 l of methylene chloride wasadded 64 g of thionylchloride in 185 ml of methylene chloride. Thereaction was slightly exothermic and the temperature was kept at 25° C.After the mixture was reacted for 4 hours the solvent was evaporated.The oily residue was dissolved in toluene and again concentrated.Finally the residue was reacted with 700 ml of ethanol. After 15 minutesa yellow solid separated which was washed with ethanol and dried. Theyield was 229 g (86%) and the melting point was 66° C.

Preparation of Compound (IIID) of Scheme (III)

To a suspension of 15 g of sodium thiosulphate in 40 ml water and 120 mlof methanol was added 54 g of compound (IIIC). The mixture was refluxedfor 4 hours. An oily layer separated. The upper layer was removed andthe oil was dissolved in 1200 ml of hexane. An orange-yellow precipitateseparated after 1 hour. The product was filtered and dried. The yieldwas 39 g (64%), and the melting point was 102.6° C.

Preparation of Compound 14A of Table 5

To a solution of 55 g of compound (IIID) in 850 ml of methanol and 250ml of water at 65° C. was added over a period of 40 minutes a solutionof 11 g of iodine in 425 ml of methanol. The product separated as anoily residue. After chromatographical purification two diastereoisomerswere obtained (Solid phase: SiO₂ ; eluent: hexane/methylenechloride7/3). The respective yields were 21.8 g (46%) and 17.2 g (37%).

Compounds 19A and 20A can be prepared by reacting the reaction productof step (2) in scheme (III) with p-dihydroxybenzyldisulphide. A similarprocedure is followed for compound 21A and is examplified by thefollowing preparation:

Preparation of Sodium S-(p-hydroxybenzyl)-thiosulfate

To a solution of 48 g of sodium S-(p-acetoxybenzyl)-thiosulfate (seeJ.O.C. 43, 1197, (1978)) in 120 ml of methanol and 40 ml of water wasadded 10 ml of HCl (1N). The reaction mixture was stirred at 50° C. for4 hours. After standing overnight a voluminous precipitate was obtained.The precipitate was collected by filtration and dried. The yield was18.8 g (46%). The melting point was 265° C.

Preparation of Bis(p-hydroxybenzyl)disulfide

To a solution of 60.5 g sodium S-(p-hydroxybenzyl)-thiosulfate in 1000ml of water was added 100 ml of H₂ SO₄ (5M) and 100 ml of H202 (35%).The formed precipitate was filtered, washed with 200 ml of H₂ O anddried. The yield was 23.9 g (34%) and the melting point was 171° C.

Preparation of Compound 21A

82.6 g of the ethylester of pivaloylacetic acid and 66 g of theethylester of 4-aminobenzoic acid were dissolved in 200 ml of xylene. Tothis solution was added 0.4 ml of lutidine. The mixture was thenrefluxed for 8 hours. Ethanol which was formed during the reaction wasremoved by distillation. After cooling the reaction mixture was dilutedwith 1 l of hexane while stirring. A white precipitate was formed whichwas isolated by filtration and subsequently dried. The precipitate wasidentified as α-pivaloyl-(p-carbethoxy)-acetanilide having a meltingpoint of 82°-85° C. The yield was 106 g.

To a solution of 29.1 g of α-pivaloyl-(p-carbethoxy)-acetanilide in 150ml of dichloromethane was dropwise added during 30 min. 8.4 ml ofsulfuryl chloride. The reaction mixture was then stirred for 9 hours atroom temperature and the solvent was subsequently removed under reducedpressure. The obtained oil was stirred with hexane and a whiteprecipitate was obtained which was filtered and dried. 31 g of α-chloro,α-pivaloyl-(4-carbethoxyacetanilide were thus obtained. The meltingpoint was 90° C.

15.6 g of α-chloro, α-pivaloyl-(4-carbethoxyacetanilide, 5.56 g ofp-dihydroxybenzyldisulphide and 10 ml of tetramethyl guanidine weredissolved in 120 ml of acetonitrile. A yellow solution was obtained thatwas stirred for 24 hours at room temperature. The reaction mixture wassubsequently acidified with 8 ml of a 5M solution of HCl and dilutedwith 130 ml of water. An oil was formed which was isolated by extractionwith dichloromethane. After removal of the dichloromethane under reducedpressure a yellow oil is obtained that was chromatographically purified.The yield was 7.9 g and the melting point was 60°-70° C.

The sensitizer releasing compounds used in accordance with the presentinvention may be present in one or more layers on the side of thesupport carrying the photosensitive silver halide. Preferably thesensitizer releasing compound is present in the layer containing thephotosensitive silver halide. The amount of releasing compound(s)comprised in the photographic material may be varied widely but ispreferably between 0.1 mmol/m² and 1 mmol/m².

The photosensitive and substantially light insensitive silver saltparticles used in accordance with the present invention may be presentin one or in separate layers. When they are present in separate layersthe order of both layers may be varied as desired with respect to thesupport and intermediate water permeable layers of e.g. gelatin may beprovided. Preferably the photosensitive and substantially lightinsensitive silver salt are present in the same layer.

To take advantage of the present invention it is important that thesubstantially light insensitive silver salt particles have a speed atleast a factor 10 preferably a factor 100 less than the photosensitivesilver halide used under the same conditions of development and exposureof the photosensitive silver halide. If the difference in speed is lessthan a factor 10 the substantially light insensitive silver salts willbe rendered developable by the exposure of the imaging element whichshould be avoided as much as possible to take most advantage of thepresent invention.

Preferred substantially light insensitive silver salts used inaccordance with the present invention are water insoluble silver saltse.g. a silver halide, bromate, molybdate, oxalate, chromate, iodate,isocyanate, thioisocyanate, cyanide, citrate, phosphate, oxide etc..Said substantially light insensitive water insoluble silver salts may beprepared using the precipitation reaction of the water soluble salt ofthe desired anion of the insoluble silver salt with a water solublesilver salt, e.g. silver nitrate, in the presence of a hydrophilicbinder. Silver halides containing at least 70 mol % of chloride arepreferred in the present invention for use as the substantially lightinsensitive silver salt particles.

As already mentioned above the substantially light insensitive silverhalide particles are preferably fine particles i.e. having a diameter ofless than 0.5 μm. The silver halide is preferably also doped with Rh³⁺,Ir⁴⁺, Cd²⁺, Zn²⁺ and/or Pb²⁺ to reduce the light sensitivity of thesilver salt. The silver halide preferably is not chemically sensitizednor spectrally sensitized i.e. a so called primitive silver halideemulsion. The silver salt particles may further be desensitized on thesurface with a desensitizing agent well known to those skilled in theart. Examples of desensitizing agents are disclosed in e.g. the U.S.Pat. Nos. 2,930,644, 3,431,111, 3,492,123, 3,501,310, 3,501,311,3,574,629, 3,579,345, 3,598,595, 3,592,653, 4,820,625, 3,933,498, and GB1,192,384. Further desensitizing agents suitable for use in accordancewith the present invention are described e.g. by P. Glafkides in "Chimieet Physique Photographique", Paul Morttel, Paris (1967). Agents thatretard the dissolution of silver salt articles by a silver halidesolvent may also be added. For example 5-nitro-indazole, ballastedmercapto-heterocyclic compounds etc. can be used for this purpose.

The photosensitive silver halide emulsion can be prepared from solublesilver salts and soluble halides according to different methods asdescribed e.g. by P. Glafkides in "Chimie et Physique Photographique",Paul Montel, Paris (1967), by G. F. Duffin in "Photographic EmulsionChemistry", The Focal Press, London (1966), and by V. L. Zelikman et alin "Making and Coating Photographic Emulsion", The Focal Press, London(1966).

The photosensitive silver halide emulsion used according to the presentinvention can be prepared by mixing the halide and silver solutions inpartially or fully controlled conditions of temperature, concentrations,sequence of addition, and rates of addition. The silver halide can beprecipitated according to the single-jet method or the double-jetmethod.

The photosensitive silver halide particles of the photographic materialused according to the present invention may have a regular crystallineform such as a cubic or octahedral form or they may have a transitionform. They may also have an irregular crystalline form such as aspherical form or a tabular form, or may otherwise have a compositecrystal form comprising a mixture of said regular and irregularcrystalline forms.

According to the present invention the photosensitive silver halideemulsion preferably consists principally of silver chloride while afraction of silver bromide is present ranging from 1 mole % to 40 mole%. However other silver halide compositions can also be used inaccordance with the present invention. The silver halide may be of thecore/shell type well known to those skilled in the art in the sense thatsubstantially all the bromide is concentrated in the core. This corecontains preferably 10 to 40% of the total silver halide precipitated,while the shell consists preferably of 60 to 90% of the total silverhalide precipitated.

The average size of the photosensitive silver halide grains may bevaried widely but preferably is between 0.2 and 5 μm, most preferablybetween 0.3 and 2 μm. The photosensitive silver halide particles arepreferably of high speed. It is furthermore advantageous that thephotosensitive silver halide particles show a rapid chemical developmenti.e. silver halide emulsions that show a complete chemical developmentwithin at least 15 s: The rate of chemical development can be easilydetermined with the following method. The silver halide emulsion layerof which the rate of chemical development is to be measured is coated toa transparent support in an amount equivalent to 2 g of AgNO₃ /m² and2.1 g of gelatin/m². The thus obtained element is exposed to a suitablelight-source and subsequently placed in a cuvette in a spectrophotometerand thermostated at 25° C. A developing solution is brought in thecuvette and the absorption at 800 nm is followed with time. From theplot of the absorption at 800 nm against time the time necessary toobtain a complete development of the sample can be determined.

The size distribution of the silver halide particles of thephotosensitive silver halide particles to be used according to thepresent invention can be homodisperse or heterodisperse. A homodispersesize distribution is obtained when 95% of the grains have a size thatdoes not deviate more than 30% from the average grain size.

Preferably during the precipitation stage Iridium and/or Rhodiumcontaining compounds or a mixture of both are added. The concentrationof these added compounds ranges from 10⁻⁸ to 10⁻³ mole per mole ofAgNO₃, preferably between 10⁻⁷ and 10⁻⁴ mole per mole of AgNO₃. Thisresults in the building in the silver halide crystal lattice of minoramounts of Iridium and/or Rhodium, so-called Iridium and/or Rhodiumdopants. As known to those skilled in the art numerous scientific andpatent publications disclose the addition of Iridium or Rhodiumcontaining compounds or compounds containing other elements of GroupVIII of the Periodic System during emulsion preparation.

The photosensitive silver halide emulsion can be chemically sensitizede.g. by adding sulphur-containing compounds during the chemical ripeningstage e.g. allyl isothiocyanate, allyl thiourea, and sodiumthiosulphate. Also reducing agents e.g. the tin compounds described inBE-P 493,464 and 568,687, and polyamines such as diethylene triamine orderivatives of aminomethane-sulphonic acid can be used as chemicalsensitizers. Other suitable chemical sensitizers are noble metals andnoble metal compounds such as gold, platinum, palladium, iridium,ruthenium and rhodium. This method of chemical sensitization has beendescribed in the article of R. KOSLOWSKY, Z. Wiss. Photogr. Photophys.Photochem. 46, 65-72 (1951).

The photosensitive silver halide emulsion of the photographic element ofthe present invention can be spectrally sensitized according to thespectral emission of the exposure source for which the photographicelement is designed.

Suitable sensitizing dyes for the visible spectral region includeroethine dyes such as those described by F. M. Hamer in "The CyanineDyes and Related Compounds", 1964, John Wiley & Sons. Dyes that can beused for this purpose include cyanine dyes, merocyanine dyes, complexcyanine dyes, complex merocyanine dyes, holopolar cyanine dyes,hemicyanine dyes, styryl dyes and hemioxonol dyes. Particularly valuabledyes are those belonging to the cyanine dyes, merocyanine dyes, complexmerocyanine dyes.

In the case of a conventional light source, e.g. tungsten light, a greensensitizing dye is needed. A preferred green sensitizing dye inconnection with the present invention is represented by the followingchemical formula: ##STR55##

In case of exposure by a red light emitting source, e.g. a LED or a HeNelaser a red sensitizing dye is used. A preferred red sensitizing dye is:##STR56##

In case of exposure by an argon ion laser a blue sensitizing dye isincorporated. A preferred blue sensitizing dye is represented by:##STR57##

In case of exposure by a semiconductor laser special spectralsensitizing dyes suited for the near infra-red required. Suitableinfra-red sensitizing dyes are disclosed in i.a. U.S. Pat. Nos.2,095,854, 2,095,856, 2,955,939, 3,482,978, 3,552,974, 3,573,921,3,582,344, 3,623,881 and 3,695,888. A preferred infra-red sensitizingdye is: ##STR58##

To enhance the sensitivity in the near infra-red region use can be madeof so-called supersensitizers in combination with infra-red sensitizingdyes. Suitable supersensitizers are described in Research Disclosure Vol289, May 1988, item 28952. A preferred supersensitizer is Compound IV ofthe Disclosure having following formula: ##STR59##

The spectral sensitizers can be added to the photosensitive silverhalide emulsions in the form of an aqueous solution, a solution in anorganic solvent or in the form of a dispersion.

The photosensitive silver halide emulsion and substantially lightinsensitive silver salt emulsions may contain the usual stabilizers e.g.homopolar or salt-like compounds of mercury with aromatic orheterocyclic rings such as mercaptotriazoles, simple mercury salts,sulphonium mercury double salts and other mercury compounds. Othersuitable stabilizers are azaindenes, preferably tetra- orpenta-azaindenes, especially those substituted with hydroxy or aminogroups. Compounds of this kind have been described by BIRR in Z. Wiss.Photogr. Photophys. Photochem. 47, 2-27 (1952). Other suitablestabilizers are i.a. heterocyclic mercapto compounds e.g.phenylmercaptotetrazole, quaternary benzothiazole derivatives, andbenzotriazole. Preferred compounds are mercapto substituted pyrimidinederivatives as disclosed in U.S. Pat. No. 3,692,527.

The silver halide emulsions may contain pH controlling ingredients.Preferably the emulsion layer is coated at a pH value below theisoelectric point of the gelatin to improve the stabilitycharacteristics of the coated layer. Other ingredients such asantifogging agents, development accelerators, wetting agents, andhardening agents for gelatin may be present. The silver halide emulsionlayer may comprise light-screening dyes that absorb scattering light andthus promote the image sharpness. Suitable light-absorbing dyes aredescribed in i.a. U.S. Pat. No. 4,092,168, U.S. Pat. No. 4,311,787, DE-P2,453,217, and GB-P 7,907,440.

Development acceleration can be accomplished with the aid of variouscompounds, preferably polyalkylene derivatives having a molecular weightof at least 400 such as those described in e.g. U.S. Pat. Nos.3,038,805 - 4,038,075 - 4,292,400.

More details about the composition, preparation and coating of silverhalide emulsions can be found in e.g. Product Licensing Index, Vol. 92,December 1971, publication 9232, p. 107-109.

The hydrophilic layers usually contain gelatin as hydrophilic colloidbinder. Mixtures of different gelatins with different viscosities can beused to adjust the theological properties of the layer. Like theemulsion layer the other hydrophilic layers are coated preferably at apH value below the isoelectric point of the gelatin. But instead of ortogether with gelatin, use can be made of one or more other naturaland/or synthetic hydrophilic colloids, e.g. albumin, casein, zein,polyvinyl alcohol, alginic acids or salts thereof, cellulose derivativessuch as carboxymethyl cellulose, modified gelatin, e.g. phthaloylgelatin etc.

The hydrophilic layers of the photographic element, especially when thebinder used is gelatin, can be hardened with appropriate hardeningagents such as those of the epoxide type, those of the ethyleniminetype, those of the vinylsulfone type e.g. 1,3-vinylsulphonyl-2-propanol,chromium salts e.g. chromium acetate and chromium alum, aldehydes e.g.formaldehyde, glyoxal, and glutaraldehyde, N-methylol compounds e.g.dimethylolurea and methyloldimethylhydantoin, dioxan derivatives e.g.2,3-dihydroxy-dioxan, active vinyl compounds e.g.1,3,5-triacryloyl-hexahydro-s-triazine, active halogen compounds e.g.2,4-dichloro-6-hydroxy-s-triazine, and mucohalogenic acids e.g.mucochloric acid and mucophenoxychloric acid. These hardeners can beused alone or in combination. The binders can also be hardened withfast-reacting hardeners such as carbamoylpyridinium salts of the type,described in U.S. Pat. No. 4,063,952.

In a preferred embodiment of the present invention an intermediatehydrophilic layer, serving as anti halation layer, is provided betweenthe support and the photosensitive silver halide emulsion layer. Thislayer can contain the same light-absorbing dyes as described above forthe emulsion layer; as alternative finely divided carbon black can beused for the same anti halation purposes as described in U.S. Pat. No.2,327,828. On the other hand, in order to gain sensitivity, image-wiselight reflecting pigments, e.g. titaniumdioxide can be present. Furtherthis layer can contain hardening agents, matting agents, e.g. silicaparticles, and wetting agents. When the photosensitive silver halide andthe substantially light insensitive silver salt are present in separatelayers the anti halation layer can be provided between both silver saltlayers.

The photographic element used according to the present invention mayfurther comprise various kinds of surface-active agents in thephotographic emulsion layer or in at least one other hydrophilic colloidlayer. Suitable surface-active agents include non-ionic agents such assaponins, alkylene oxides e.g. polyethylene glycol, polyethyleneglycol/polypropylene glycol condensation products, polyethylene glycolalkyl ethers or polyethylene glycol alkylaryl ethers, polyethyleneglycol esters, polyethylene glycol sorbitan esters, polyalkylene glycolalkylamines or alkylamides, silicone-polyethylene oxide adducts,glycidol derivatives, fatty acid esters of polyhydric alcohols and alkylesters of saccharides; anionic agents comprising an acid group such as acarboxy, sulpho, phospho, sulphuric or phosphoric ester group;ampholytic agents such as aminoacids, aminoalkyl sulphonic acids,aminoalkyl sulphates or phosphates, alkyl betaines, and amine-N-oxides;and cationic agents such as alkylamine salts, aliphatic, aromatic, orheterocyclic quaternary ammonium salts, aliphatic or heterocyclicring-containing phosphonium or sulphonium salts. Preferably compoundscontaining perfluorinated alkyl groups are used. Such surface-activeagents can be used for various purposes e.g. as coating aids, ascompounds preventing electric charges, as compounds improvingslidability, as compounds facilitating dispersive emulsification and ascompounds preventing or reducing adhesion.

The photographic element of the present invention may further comprisevarious other additives such as e.g. compounds improving the dimensionalstability of the photographic element, UV-absorbers, spacing agents ormatting agents and plasticizers. Preferred spacing agents are SiO₂particles having an average size of from 0.8 μm to 15 μm. These spacingagents may be present in one or more layers comprised on the support ofthe photographic material.

Suitable additives for improving the dimensional stability of thephotographic element are e.g. dispersions of a water-soluble or hardlysoluble synthetic polymer e.g. polymers of alkyl (meth)acrylates,alkoxy(meth)acrylates, glycidyl (meth)acrylates, (meth)acrylamides,vinyl esters, acrylonitriles, olefins, and styreries, or copolymers ofthe above with acrylic acids, methacrylic acids, Alpha-Beta-unsaturateddicarboxylic acids, hydroxyalkyl (meth)acrylates, sulphoalkyl(meth)acrylates, and styrene sulphonic acids.

According to the present invention there is provided a method forobtaining an image with the photographic material described above.According to this method the photographic material of the presentinvention is information-wise exposed and subsequently developed in thepresence of developing agents. Suitable developing agents for theexposed silver halide are e.g. hydroquinone-type and1-phenyl-3-pyrazolidone-type developing agents as well asp-monomethylaminophenol and derivatives thereof. Preferably used is acombination of a hydroquinone-type and 1-phenyl-3-pyrazolidone-typedeveloping agent whereby the latter is preferably incorporated in one ofthe layers comprised on the support of the photographic material. Apreferred class of 1-phenyl-3-pyrazolidone-type developing agents isdisclosed in the European patent application number 449340. It was foundthat most advantage of the present invention is taken when at least oneof the there disclosed developing agents are present in the photographicmaterial of the present invention preferably in the layer(s) comprisingthe photosensitive and/or substantially light insensitive silver saltparticles. Other type of developing agents suitable for use inaccordance with the present invention are reductones e.g. ascorbic acidderivatives. Such type of developing agents are disclosed in theunpublished European patent application number 91200311.8.

The developing agent or a mixture of developing agents can be present inan alkaline processing solution and/or in the photographic material. Incase the developing agent or a mixture of developing agents is containedin the photographic material, the processing solution can be merely anaqueous alkaline solution that initiates and activates the development.

The pH of the alkaline processing solution is preferably between 10 and13. The desired pH of the processing solution can be reached byincorporating alkaline substances in the processing solution. Suitablealkaline substances are inorganic alkali e.g. sodium hydroxide,potassium carbonate or alkanolamines or mixtures thereof. Preferablyused alkanolamines are tertiary alkanolamines e.g. those described inEP-A-397925, EP-A-397926, EP-A-397927, EP-A-398435 and U.S. Pat. No.4.632.896. A combination of alkanolamines having both a pk_(a) above orbelow 9 or a combination of alkanolamines whereof at least one has apk_(a) above 9 and another having a pk_(a) of 9 or less may also be usedas disclosed in the Japanese patent applications laid open to the publicnumbers 73949/61, 73953/61, 169841/61, 212670/60, 73950/61, 73952/61,102644/61, 226647/63, 229453/63, U.S. Pat. No. 4,362,811, U.S. Pat. No.4,568,634 etc.. The concentration of these alkanolamines is preferablyfrom 0.1 mol/l to 0.9 mol/l.

According to the present invention best results are obtained when thephotographic element of the present invention is developed in thepresence of a silver halide solvent. Preferably used silver halidesolvents are water soluble thiosulphate compounds such as ammonium andsodium thiosulphate, or ammonium and alkali metal thiocyanates. Otheruseful silver halide solvents (or "complexing agents") are described inthe book "The Theory of the Photographic Process" edited by T. H. James,4th edition, p. 474-475 (1977), in particular sulphites and uracil.Further interesting silver halide complexing agents are cyclic iraides,preferably combined with alkanolamines, as described in U.S. Pat. No.4,297,430 and U.S. Pat. No. 4,355,090. 2-mercaptobenzoic acidderivatives are described as silver halide solvents in U.S. Pat. No.4,297,429, preferably combined with alkanolamines or with cyclic iraidesand alkanolamines. Dialkylmethylenedisulfones can also be used as silverhalide solvent.

The silver halide solvent is preferably present in the processingsolution but may also be present in one or more layers comprised on thesupport of the photographic element. When the silver halide solvent isincorporated in the photographic material it may be incorporated as asilver halide solvent precursor as disclosed in e.g. Japanese publishedunexamined patent applications no. 15247/59 and 271345/63, U.S. Pat. No.4,693,955 and U.S. Pat. No. 3,685,991.

The processing solution for use in accordance with the present inventionmay comprise other additives such as e.g. thickeners, preservatives,detergents e.g. acetylenic detergents such as surfynol 104, surfynol465, surfynol 440 etc. all available from Air Reduction Chemical CompanyNew York.

The photographic material of the present invention can be used in avariety of application fields e.g. for producing images according to theDTR-process, for producing lithographic printing plates according to theDTR-process, for scanning exposure, in Computer Output to Microfilm(COM) applications etc. The use of the photographic material of thepresent invention in some of these application fields will be describedin more detail in the following embodiments.

According to a first application the photographic material of thepresent invention can be used in a DTR-process to produce negative orpositive images. The principles of the silver complex diffusion transferreversal process have been described e.g. in U.S. Pat. No. 2,352,014 andin the book "Photographic Silver Halide Diffusion Processes" by AndreRott and Edith Weyde--The Focal Press--London and New York, (1972).

In the DTR-process non-developed silver halide of an image-wise exposedphotographic silver halide emulsion layer material is transformed with asilver halide solvent into soluble silver complex compounds which areallowed to diffuse into an image-receiving layer and are reduced thereinwith a developing agent, generally in the presence of physicaldevelopment nuclei, to form a silver image having reversed image densityvalues with respect to the silver image obtained in the exposedphotographic material.

The DTR-process was initially intended for office copying purposes buthas found now wide application in the graphic art field, moreparticularly in the production of screened prints from continuous toneoriginals. For processing DTR-materials according to the presentembodiment use can be made of processing solutions described aboveprovided of course that a silver halide solvent of the type described ispresent in the processing solution and/or in one or more layers of theDTR-material e.g. the image-receiving layer. When the silver halidesolvent is incorporated in the photographic material it may beincorporated as a silver halide solvent precursor as disclosed in e.g.Japanese published unexamined patent applications no. 15247/59 and271345/63, U.S. Pat. No. 4,693,955 and U.S. Pat. No. 3,685,991. Whenfairly low gradation images for continuous tone reproduction have to beproduced preference is given to developing agent combinations asdescribed in U.S. Pat. Nos. 3,985,561 and 4,242,436.

Processing of the DTR-material according to the present invention ispreferably carried out using a single processing solution. However thephotographic material according to the present embodiment may also beprocessed using two processing solutions. In the latter case only thesecond processing liquid used to process contains a silver halidesolvent(s).

The alkaline processing solution for use in accordance with thisembodiment preferably contains (a) silver image toning agent(s)providing a neutral (black) image tone to the DTR-produced silver imagein the image-receiving layer. A survey of suitable toning agents isgiven in the above mentioned book of Andre Rott and Edith Weyde, p.61-65, preference being given to 1-phenyl-5-mercapto-tetrazole,tautomeric structures and derivatives thereof such as1-(2,3-dimethylphenyl)-5-mercapto-tetrazole,1-(3,4-dimethylcyclohexyl)-5-mercapto-tetrazole, 1-(4-methylphenyl)-5-mercapto-tetrazole, 1-(3-chloro-4-methylphenyl)-5-mercapto-tetrazole, 1-(3,4-dichlorophenyl)-5-mercapto-tetrazole.Other suitable black toning agents for use in accordance with thepresent embodiment are those disclosed in the European patentapplications 218752, 208346, 218753 and U.S. Pat. No. 4683189.

For DTR-processing the aqueous alkaline processing solution may comprise(a) toning agent(s) in a concentration in a range e.g. from 30 mg to 200mg per liter. Said toning agents may also at least partially be presentin the image receiving layer and/or in a layer in water permeablerelationship therewith.

Other additives for the processing solution are thickening agents, e.g.hydroxyethylcellulose and carboxymethylcellulose, fog inhibiting agents,e.g. potassium bromide, potassium iodide and a benzotriazole,calcium-sequestering compounds, wetting agents, e.g. block copolymers ofethyleneoxide or of propylene oxide, anti-sludge agents, and hardenersincluding latent hardeners.

The DTR-image can be formed in the image-receiving layer of a sheet orweb material being a separate element with respect to the photographicsilver halide emulsion material or in a so-calledsingle-support-element, also called moro-sheet element or unitaryDTR-material, which contains at least one photographic silver halideemulsion layer and the image-receiving layer in water permeablerelationship therewith, e.g. on top of each other or separated by a thinwater permeable stripping layer or alkali-degradable interlayer asdescribed e.g. in U.S. Pat. No. 3,684,508 or wherein the photographicsilver halide emulsion layer is optically masked from theimage-receiving layer, e.g. with a white water permeable pigment layeras described e.g. in U.S. Pat. Nos. 3,607,270 and 3,740,220.

When the DTR-image is formed on a separate sheet called image receivingmaterial the information-wise exposed photographic material is processedin the processing liquid while in contact with said receiving material.Alternatively the processing liquid may be applied to either theimage-receiving material or photographic material before contacting bothelements. Both elements are usually kept in contact with each other for30 s to 1 min..

The support of the image receiving material and/or photographic materialmay be opaque or transparent, e.g. a paper support or resin support. Theimage receiving layer comprises for best imaging results physicaldevelopment nuclei normally in the presence of a protective hydrophiliccolloid, e.g. gelatin, polyvinyl alcohol, polyvinyl pyrrolidone,poly(meth)acryl amide etc. or mixtures thereof, and/or colloidal silica.

Preferred development nuclei are sulphides of heavy metals e.g.sulphides of antimony, bismuth, cadmium, cobalt, lead, nickel,palladium, platinum, silver, and zinc. Especially suitable developmentnuclei are NiS.Ag₂ S nuclei as described in U.S. Pat. No. 4,563,410.Other suitable development nuclei are salts such as e.g. selenides,polyselenides, polysulphides, mercaptans, and tin (II) halides. Heavymetals or salts thereof and fogged silver halide are suitable as well.The complex salts of lead and zinc sulphides are active both alone andwhen mixed with thioacetamide, dithiobiuret, and dithiooxamide. Heavymetals, preferably silver, gold, platinum, palladium, and mercury can beused in colloidal form.

Most of the DTR-image receiving materials now available on the marketare composed of two or even three layers. Such materials normallycontain on top of the nuclei containing layer a layer which itselfcontains no nuclei and otherwise has the same composition as the nucleicontaining layer and mainly serves to ensure good contact between thelight sensitive and image receiving material during transfer. Moreover,after drying this layer provides a protective coating for the imagereceiving layer containing the silver image. It further preventsbronzing or plumming of the black image areas in preventing theprotruding of silver from the image receiving layer in the form of aglossy silver mirror (ref. the above mentioned book p. 50).

According to a preferred mode of the present embodiment in theimage-receiving element the development nuclei containing layer and/orhydrophilic colloid layer in water permeable relationship or a backlayer at the side of the support opposite to that carrying the imagereceiving layer contains at least part of the silver image toningagents. Such procedure results actually in automatic replenishment oftoning agent in the processing liquid. The same applies at least partlyfor the replenishment of the developing agent(s) and silver halidecomplexing agent(s).

At least a part of said silver image toning agents may be present in thesilver halide emulsion material to be developed. Such means that in apractical embodiment at least one of the image toning agents may be usedin a hydrophilic water permeable colloid layer, e.g. anti halation layerat the side of the support opposite to the side coated with thephotosensitive silver halide emulsion layer or between the support andthe silver halide emulsion layer. The coverage of said silver imagetoning agents in said anti halation layer is preferably in the range of1 mg/m² to 20 mg/m².

Said layer at the side of the support opposite to the side coated withthe photosensitive silver halide emulsion layer may also containanti-sludge agents for reducing the contamination of the processingliquid. Suitable anti-sludge agents are disclosed in e.g. EP-223883,U.S. Pat. No. 3,438,777, BE-P-606550 and GB-P-1120963. Furtheranti-sludge agents suitable for use in accordance with the presentinvention correspond to the following general formula:

    R--SH

wherein R represents an alkyl or alkylaryl group containing at least 7carbons in a straight line.

The transfer behaviour of the complexed silver largely depends on thethickness of the image-receiving layer and the kind of binding agent ormixture of binding agents used in the nuclei containing layer. In orderto obtain a sharp image with high spectral density the reduction of thesilver salts diffusing into the image receiving layer must take placerapidly before lateral diffusion becomes substantial. An image-receivingmaterial satisfying said purpose is described in U.S. Pat. No.4,859,566.

A white appearance of the image background even when a yellow stainwould appear on storage is obtained by incorporation of opticalbrightening agents in the support, image-receiving layer and/orinterlayer between the support and the image-receiving layer.

In the image-receiving layer and/or in an undercoat gelatin is usedpreferably as hydrophilic colloid. In these layer(s) gelatin is presentpreferably for at least 60% by weight and is optionally used inconjunction with an other hydrophilic colloid, e.g. polyvinyl alcohol,cellulose derivatives, preferably carboxymethyl cellulose, dextran,gallactomannans, alginic acid derivatives, e.g. alginic acid sodium saltand/or water soluble polyacrylamides.

The image-receiving layer and/or a hydrophilic colloid layer inwater-permeable relationship therewith may comprise a silver halidedeveloping agent and/or silver halide solvent, e.g. sodium thiosulphatein an amount of approximately 0.1 g to approximately 4 g per m².

The image-receiving layer or a hydrophilic colloid layer inwater-permeable relationship therewith may comprise colloidal silica.

The image-receiving layer may contain as physical developmentaccelerators, in operative contact with the developing nuclei, thioethercompounds such as those described e.g. in DE-A-1,124,354; U.S. Pat. No.4,013,471; U.S. Pat. No. 4,072,526; and in EP 26520.

When applying an optical brightening agent in the image-receivingmaterial preference is given to an optical brightening agent that isinherently by its structure resistant to diffusion or is made resistantto diffusion by use in conjunction with another substance wherein it isdissolved or whereto it is adsorbed.

For example, to make an optical brightening agent resistant to diffusionone of the following techniques may be applied.

According to a first technique known from colour photography the opticalbrightening compound is substituted with a long chain aliphatic residueand ionomeric residue as is known in the synthesis of diffusionresistant colour couplers.

According to a second technique an optical brightening agent of theoleophilic type is incorporated in droplets of a water-immisciblesolvent, so-called "oilformer", e.g. dibutylphthalate.

According to a third technique the optical brightening agent is used inconjunction with a polymeric hydrophilic colloid adsorber, a so-calledtrapping agent, e.g. poly-N-vinylpyrrolidinone as described e.g. in U.S.Pat. Nos. 3,650,752, 3,666,470 and 3,860,427 and published Europeanpatent application 0 106 690.

According to a fourth technique latex compositions are used whereinlatex particles are loaded, i.e. contain in dissolved and/or adsorbedstate an optical brightening agent as described e.g. in GermanOffenlegungsschrift (DE-OS) 1,597,467 and in U.S. Pat. No. 4,388,403.

The image-receiving layer and/or other hydrophilic colloid layer of animage-receiving material used in a DTR-process according to the presentembodiment may have been hardened to some extent to achieve enhancedmechanical strength. Appropriate hardening agents for hardening thenatural and/or synthetic hydrophilic colloid binding agents in theimage-receiving layer include e.g. formaldehyde, glyoxal, mucochloricacid, and chrome alum. Other suitable hardening agents for hardening thehydrophilic colloid binding agents in the image-receiving layer arevinylsulphonyl hardeners, e.g. as described in Research Disclosure22,507 of January 1983.

According to a second application the photographic material can be usedfor manufacturing a lithographic printing plate precursor and formanufacturing a printing plate using the DTR-process. A DTR-imagebearing material can be used as a planographic printing plate whereinthe DTR-silver image areas form the water-repellant ink-receptive areason a water-receptive ink-repellant surface. The DTR-image can be formedin the image-receiving layer of a sheet or web material which is aseparate element with respect to the photographic silver halide emulsionmaterial (a so-called two-sheet DTR element) disclosed in e.g.DE-A-2.346.378 or in the image-receiving layer of a so-calledsingle-support-element, also called mono-sheet element, which containsat least one photographic silver halide emulsion layer integral with animage-receiving layer in water permeable relationship therewith. It isthe latter mono-sheet version which is preferred for the preparation ofoffset printing plates by the DTR method.

Todate on the market lithographic printing plates made according to theDTR-process are positive working lithographic printing plates i.e. thenon-exposed areas of a negative working silver halide will correspond tothe printing areas on the plate. Most originals used for making alithographic printing plate require reversal of the image which wouldnot be required with a negative working printing plate. Furthermore,since only the image-areas have to be exposed on a negative workinglithographic printing plate time can be saved in the imaging of such aprinting plate with a laser. As described above the present inventionoffers the possibility to obtain a negative working lithographicprinting plate without loss of speed.

According to the method of the present invention for making alithographic printing plate an imaging element containing aphotosensitive silver halide and substantially insensitive silver halidehaving a speed at least a factor 10 less than said photosensitive silverhalide and a releasing compound capable of releasing a sensitizer isinformation-wise exposed and developed in the presence of (a) developingagent(s) and (a) silver halide solvent(s) while in contact with an imagereceiving layer that may be contained on a separate support, a so-calledtwo-sheet DTR-material or may be contained in the imaging element a socalled monosheet DTR-material. Subsequent thereto the developed printingplate is preferably treated with a neutralization solution containingbuffer substances to neutralize the alkaline plate after treatment withthe developing liquid.

Normally in lithographic printing greasy inks are employed. So, toobtain good prints it is necessary that the difference in oleophilic andhydrophilic (oleophobic) properties of the image and background surfaceis sufficiently distinct so that when water and ink are applied duringthe printing process, the image will accept sufficient ink leaving thebackground clean.

Suitable methods to enhance the differentiation in ink acceptancebetween the hydrophobic silver image parts and the hydrophilic non-imageparts are as follows. Use can be made of so-called hydrophobizing agentsto improve the ink acceptance of the silver image parts and which can bepresent, depending on the case, in one of the normal processingsolutions of the DTR process, or in a separate solution, a so-calledlithographic fixer. For example, U.S. Pat. No. 3,776,728 describes i.a.developer solutions which contain a heterocyclic mercapto-compound, e.g.a 2-mercapto-1,3,4-oxadiazole derivative, as hydrophobizing agent. U.S.Pat. No. 4,563,410 describes hydrophobizing liquids containing one ormore mercaptotriazole or mercaptotetrazole derivatives or mixturesthereof.

Another method of enhancing the hydrophobic character of the silverimage that can be used in accordance with the present invention consistsin maximizing the ratio of the amount of development nuclei to theamount of hydrophilic binder, e.g. gelatin, in the development nucleicontaining surface layer where the DTR-image is formed. For example U.S.Pat. No. 3,728,114 describes a direct positive sheet suitable forproducing an offset printing plate which contains in its surface layerat most 30% of a high molecular weight compound, e.g. gelatin, relativeto the weight of the nuclei.

Two types of mono-sheet DTR lithographic printing plate precursors areknown and can be used in accordance with the present invention. A firsttype of lithographic printing plate precursor comprises a hydrophilicsupport e.g. an anodized aluminium support provided with animage-receiving layer and a photosensitive silver halide emulsion,substantially light insensitive silver salt particles and a sensitizerreleasing compound. This lithographic printing plate precursor is thenimage-wise exposed and developed according to the DTR-process. Aftersaid development the layers above the image-receiving layer are removedby rinsing with water so that the silver image formed in theimage-receiving layer is exposed and can be used to print.

The second type of lithographic printing plate precursor comprises on asupport a photosensitive silver halide emulsion layer, substantiallylight insensitive silver salts, a sensitizer releasing compound and animage receiving layer as the outermost layer. According to the methodfor obtaining a lithographic printing plate with this type of precursorsaid precursor is information-wise exposed and development according toDTR-process and the imaged lithographic printing plate precursor is usedto print without separation of the now useless silver halide emulsionlayer. Commercially available DTR materials according to this methodwhich can be processed to lithographic printing plates are marketed e.g.by MITSUBISHI PAPER MILLS LTD under the trade name SILVERMASTER and byAGFA-GEVAERT N.V. under the trade name SUPERMASTER.

The image-receiving layer for use in accordance with the presentembodiment is preferably a layer of physical development nuclei andwhich layer is preferably substantially free of binding agents. Physicaldevelopment nuclei suitable for use in accordance with this embodimentare the physical development nuclei described above. Preferably usedphysical development nuclei are heavy metal sulphides e.g. palladiumsulphide.

Suitable supports for the lithographic printing plate precursor aremetal supports preferably aluminium or zinc, paper supports preferablypolyethylene coated paper supports disclosed in e.g. Japanese patent no.1.030.140, polyester film supports preferably polyethyleneterephthalate.

Metal supports are especially suitable for lithographic printing platesaccording to the first type. For example an anodized aluminium foil canbe provided with a layer containing physical development nuclei directlyto the support. To this layer is then preferably applied a layercontaining a non-proteinic hydrophilic film forming polymer, latexparticles or mixtures thereof as disclosed in EP-A-90202900.8 andEP-A-410500. To the thus obtained element a layer containing thephotosensitive silver halide particles, the substantially lightinsensitive silver salt particles and the releasing compound is finallyapplied. According to a variation the photosensitive silver halideparticles and the substantially light insensitive silver salt particlescan be present in separate layers the releasing compound then beingpresent in one or both of these layers. The arrangement of theseseparate layers being preferably so that the layer containing thephotosensitive silver halide particles is the remotest from the support.The releasing compound may also be present in other layers comprised onthe photosensitive side of the support.

When a paper support or polyester film support is used the layerarrangement described above is reversed so that the physical developmentnuclei layer is the remotest from the support. A lithographic printingplate precursor of the second type described above is thus obtained.

In the past several developments that can be used in accordance with thepresent invention have taken place for improving the storage stability,printing properties, photographic properties etc. of these printingplates and/or printing plate precursors of the second type. It has beenfound advantageous with respect to storage stability to includedeveloping agents of the hydroquinone type and of the1-phenyl-3-pyrazolidone type in the photographic material in a ratio byweight of the hydroquinone type to the 1-phenyl-pyrazolidone type notmore than 2.5 and preferably between 2.0 and 0.8.

Preferably the lithographic printing plate precursor also includes socalled matting agent in a hydrophilic base layer comprised between thesupport and the subsequent layers comprised on the support. The mattingagent may also be included in other layer such as the layer(s)containing the photosensitive and/or substantially light insensitivesilver salt particles but preferably at least 80% of the total amount isincluded in the base layer. Suitable matting agent for use in accordancewith the present embodiment are organic or inorganic particles having anaverage size of 0.8 μm to 20 μm preferably between 2 μm and 10 μm.Mixtures of matting agents having different sizes may also be used.Examples of inorganic particles are SiO₂, TiO₂, Al₂ O₃, clay etc.Examples of organic particles are latex particles of homopolymers and/orcopolymers of (meth)acrylate.

With respect to the printing endurance it is further advantageous toinclude a hydrophilic colloid layer contiguous to the image-receivinglayer. Especially good results are obtained when said hydrophiliccolloid layer is used in accordance with the present invention. Saidhydrophilic colloid layer is preferably gelatin. To increase theprinting endurance it is also known to include a benztriazole in thelithographic printing plate precursor and/or the processing solution asdisclosed in e.g. U.S. Pat. No. 4,824,760.

According to a third application of the present invention thephotographic material can be used for preparing a positive workingsilver halide photographic material having a high speed. Such type ofmaterials are commonly employed in COM-applications as well as in thegraphic arts field. Todate positive working materials for use inCOM-applications are based on direct positive silver halide emulsions.These type of silver halide emulsions are however less sensitive thannegative silver halide emulsions.

Since it is possible according to the present invention to obtain apositive working photographic material with a negative photosensitivesilver halide emulsion a high speed positive working photographicmaterial can be obtained. For this purpose a support e.g. a paper orresin support is provided with a layer comprising a negative workingphotosensitive silver halide emulsion, substantially light insensitivesilver salt particles and a releasing compound that is capable ofreleasing a chemical sensitizer mainly in the non-exposed areas. Duringdevelopment the chemical sensitizer will be released in the non-exposedareas where the chemical sensitizer causes the development of thesubstantially light insensitive and possibly the photosensitive silversalt. However in the exposed areas the photosensitive silver halide willalso develop thus yielding a certain density in the exposed areas whichis not desired. To decrease the density in the exposed areas the amountof photosensitive silver halide is kept as low as possible preferablybelow 0.5 g of AgNO₃ /m² and the average grain size is preferably morethan 0.4 μm. To further reduce the density in the exposed areas use canbe made of compounds that release a development inhibitor in the exposedareas upon development. For example development inhibitor releasingcompounds disclosed in e.g. EP-A-347849, the U.S. Pat. Nos. 3,148,062,3,227,554, 3,733,201, 3,617,291, 3,980,479, 3,933,500, 4,248,962,4,409,323 and 4,684,604 can be used.

Said development step is preferably followed by a washing step, a fixingstep and another washing or stabilizing step. The first washing step maybe omitted.

According to a variation of the present embodiment the photosensitiveand substantially light insensitive silver salt particles are present inseparate layers the preferred mode however being the above describedmode.

According to a fourth application of the present invention a negativeworking photographic material may be prepared in a similar way asdescribed in the third embodiment with the difference however that areleasing compound is comprised in the photographic material thatreleases a chemical sensitizer during development mainly in the exposedareas of the negative working photosensitive silver halide.

The present invention will now be illustrated with the followingexamples without limiting the present invention thereto. All parts areby weight unless otherwise specified. The sizes of the silver halidegrains mentioned in these examples is expressed as the average diameterof all silver halide grains. By the diameter of a silver halide grain ismeant the diameter of a hypothetical sphere with an equivalent volume asthe corresponding silver halide grain.

EXAMPLE 1

Preparation of the substantially light insensitive silver halideemulsion.

    ______________________________________                                        Solution A (40° C.):                                                                     water      1000   ml                                                          AgNO.sub.3 332    g                                         Solution B (40° C.):                                                                     water      100    ml                                                          NaCl       42.3   g                                         Solution C (40° C.):                                                                     water      900    ml                                                          KBr        5.6    g                                                           NaCl       377    g                                         Solution D (40° C.):                                                                     gelatin    50     g                                         ______________________________________                                    

Solution D was brought to pH 4.0 with a sulfuric acid solution and to apAg of 105 mV with a sodium chloride solution. Subsequently solution Awas added at a constant rate, while solution B was added at a rate so asto keep the pAg at 105 reV. Solution A was further added at anaccelerating rate, while solution C was added at a rate sufficient tokeep the pAg constant. The resulting silver halide emulsion wasprecipitated by adding polystyrene sulphonic acid. The precipitate wasrinsed several times and redispersed by adding 180 g of gelatin per 2.2kg of precipitate. A substantially light insensitive silver halideemulsion containing 99 mol % of silver chloride and 1 mol % of silverbromide was thus obtained. The average grain size was 0.155 μm.

Preparation of the photosensitive silver halide emulsion.

    ______________________________________                                        Solution E (20° C.):                                                                    AgNO.sub.3   1.7    g                                                         water        1000   ml                                       Solution F (20° C.):                                                                    water        250    ml                                                        NaCl         11.3   g                                        Solution G (40° C.):                                                                    water        995    ml                                                        AgNO.sub.3   33     g                                        Solution H (40° C.):                                                                    water        1250   ml                                                        NaCl         668    g                                                         KBr          4.4    g                                                         H.sub.2 SO.sub.4 (1N)                                                                      47.5   ml                                       Solution I (58° C.):                                                                    NaCl         5.66   g                                                         gelatin      90     g                                                         H.sub.2 SO.sub.4 (1N)                                                                      24     ml                                                        water        2500   ml                                       ______________________________________                                    

Solution E and F were simultaneously added to solution I in 3 min..After 10 min. 42 μg rhodium(III)hexachloride was added. Solution G wasthen added to solution I in 5 min. and subsequently solution H was addedto solution I in 8 min. Physical ripening was carried out for 40 min. at65° C., whereafter 0.6 ml of a potassium iodide solution (3 mol/l) wereadded. The silver halide emulsion was subsequently ripened with gold andthiosulphate and precipitated with polystyrene sulphonic acid. Afterwashing the silver halide emulsion was stabilized with triazaindolizineand redispersed with 160 g of gelatin per 566 kg of silver expressed asAgNO₃. The silver halide emulsion was then spectrally sensitized with anortho sensitizer. A silver halide emulsion with a composition of 98.5%AgCl, 1.3% AgBr and 0.2% AgI was obtained with an average grain size of0.41 μm.

Preparation of a lithographic printing plate precursor.

To a polyethylene terephthalate film support coated with a hydrophilicadhesion layer was coated a layer containing a mixture of the abovedescribed photosensitive silver halide emulsion and the above describedsubstantially light insensitive silver halide emulsion in a total amountof silver halide corresponding to 2.8 g AgNO₃ /m². 18% of the totalamount of AgNO₃ in the layer corresponded to the photosensitive silverhalide. This layer further contained 0.446 mmol/m² of hydroquinone, 0.34mmol/m² of a 1-phenyl-3pyrazolidone and a dispersion of compound 14A oftable 5 in an amount of 0.467 mmol/m². To the thus obtained element wasthen applied a finishing layer of gelatin in an amount of 0.6 g gelatinper m² and a layer of PdS physical development nuclei.

Preparation of the lithographic printing plate.

The thus obtained lithographic printing plate precursor was image-wiseexposed through a negative original for 1.3 s with a halogen lightsource and subsequently processed as follows:

15 s in an activator solution with the following composition:

    ______________________________________                                        cyclohexanedimethylol   25     g/l                                            methylpropylpropaandiol 25     g/l                                            Na.sub.2 CO.sub.3       14     g/l                                            NaOH                    70.9   g/l                                            ______________________________________                                    

30 s in a transfer developer with the following composition:

    ______________________________________                                        NaOH                      30    g/l                                           hydroquinone              13    g/l                                           1-phenyl-4,4-dimethyl-3-pyrazolidone                                                                    5     g/l                                           KSCN                      7     g/l                                           5-heptyl-2-mercapto-1,3,4-oxadiazole                                                                    0.5   g/l                                           ______________________________________                                    

30 s in a stabilising liquid with the following composition:

    ______________________________________                                        NaH.sub.2 PO.sub.4.2H.sub.2 O                                                                          60    g/l                                            Na.sub.2 HPO.sub.4. 12H.sub.2 O                                                                        10    g/l                                            Na.sub.2 SO.sub.3        5     g/l                                            Cysteine.HCl.H.sub.2 O   1     g/l                                            Ammoniumperfluorocaprylate                                                                             0.2   g/l                                            ______________________________________                                    

The thus obtained printing plate was installed on an ABDIck 9850printing press. Up to 10000 copies of good quality could be printedusing ABDick 1020 ink and a conventional fountain solution.

EXAMPLE 2

An imaging element was prepared by coating a polyethyleneterephthalatefilm support coated with a hydrophilic adhesion layer with a layercontaining a mixture of the photosensitive silver halide emulsion andthe substantially light insensitive silver halide emulsion, bothdescribed in example 1, in a total amount of silver halide correspondingto 2.8 g AgNO₃ /M². 18% of the total amount of AgNO₃ in the layercorresponded to the photosensitive silver halide. To the thus obtainedelement was coated a finishing layer of gelatin in an amount of 0.6 ggelatin per m².

The thus obtained imaging element was image-wise exposed through anegative original for 1.3 s with a halogen light source and subsequentlyprocessed with the activator solution (15 s) and the transfer developer(30 s) described in example 1. The transmission density obtained in theexposed areas was 0.5 and 2.6 in the non-exposed areas.

EXAMPLE 3

An imaging element was prepared as in example 2 with the exceptionhowever that the photosensitive silver halide emulsion was replaced witha silver halide emulsion containing 99.5 mol % AgCl and 0.5 mol % AgBrhaving a grain size of 0.6 μm. The latter silver halide emulsion wasprepared in a similar way as in example 1. The amount of photosensitivesilver halide emulsion in the layer was 12.6% of the total amount ofsilver halide expressed as AgNO₃.

The obtained imaging element was image-wise exposed and processed as inexample 2 with the exception that 1-phenyl-4,4-dimethyl-3-pyrazolidonewas omitted in the transfer developer. The transmission density obtainedin the exposed area was 3.1 and 0.33 in the non-exposed areas.

A similar image-wise exposed imaging element could also be processedusing a single processing bath with the following composition:

    ______________________________________                                        cyclohexanedimethylol     25     g/l                                          methylpropylpropaandiol   25     g/l                                          Na.sub.2 CO.sub.3         14     g/l                                          NaOH                      70.9   g/l                                          Na.sub.2 SO.sub.3         30     g/l                                          1-hydroxymethyl-5,5-dimethylhydantoine                                                                  16     g/l                                          phentyl-pyridinium chloride                                                                             2      g/l                                          KSCN                      2      g/l                                          5-heptyl-2-mercapto-1,3,4-oxadiazole                                                                    0.15   g/l                                          hydroquinone              4      g/l                                          ______________________________________                                    

An image was obtained having a transmission density of 0.4 in theexposed areas and 2.12 in the non-exposed areas.

EXAMPLE 4

A photosensitive silver halide emulsion containing 2.7 mol % of AgBr and97.3 mol % of AgCl was prepared using the double jet method. The averagesize of the silver halide particles was 1.35μm.

A substantially light insensitive silver chloride emulsion was preparedaccording to the double jet method. The average size of the silverchloride particles was 0.086 μm. The silver chloride particles weredoped with rhodium(III)chloride in an amount of 0.169 mmol per tool ofAgNO₃ to reduce their speed.

A comparative imaging element was prepared by coating a mixture of thisphotosensitive and substantially light insensitive silver halideemulsion in a total amount of silver halide corresponding to 2.5 g AgNO₃/m² to a polyethylene terephthalate film support coated with ahydrophilic adhesion layer. The total amount of binder (gelatin) in thislayer was 2.12 g/m². 20% of the total amount of AgNO₃ corresponded tophotosensitive silver halide. This layer further contained 0.5mmol/m² ofa hydroquinone and 0.75 mmol/m² of a 1-phenyl-3-pyrazolidone. To thethus obtained element was coated a layer of gelatin in an amount of 0.5g/m² containing 3 mmol/m² of a hydroquinone.

A second imaging element according to the invention was prepared similarto the comparative imaging element with the exception however that0.5mmol/m² of compound 14A mentioned in table 5 was incorporated in thelayer containing the photosensitive silver halide.

The thus obtained imaging elements were information-wise exposed andsubsequently developed with the following processing solution for 2min.:

    ______________________________________                                        sodium carbonate (anhydrous)                                                                           14 g/l                                               sodium hydroxide         69 g/l                                               uracil                   0.01M                                                ______________________________________                                    

and finally fixated with a solution containing 138 g/l of athiosulphate.

The transmission density measured in the exposed areas for thecomparative imaging element was 0.2 and 0.09 in the non-exposed areas.The imaging element according to the invention yielded a density valueof 0.4 in the exposed areas and 2.5 in the non-exposed areas.

An information-wise exposed imaging element according to the inventionas described in this example was developed with the following processingsolution for 30 s:

    ______________________________________                                        sodium carbonate (anhydrous)                                                                          14 g/l                                                sodium hydroxide        69 g/l                                                uracil                  0.05M                                                 hydroquinone            4.33 g/l                                              1-phenyl-3-pyrazolidone 1.57 g/l                                              ______________________________________                                    

and fixed with a solution containing 138 g/l of a thiosulphate,

The density measured in the exposed areas was 0.13 and 1.45 in thenon-exposed areas.

EXAMPLE 5

A photosensitive silver halide emulsion containing 2.7 mol % of AgBr and97.3 mol % of AgCl was prepared using the double jet method. The averagesize of the silver halide particles was 1.08 μm.

A substantially light insensitive silver chloride emulsion was preparedaccording to the double jet method, The average size of the silverchloride particles was 0.091 μm. The silver chloride particles weredoped with rhodium(III)chloride in an amount of 160 ppm to reduce theirspeed,

An imaging element was prepared by coating a mixture of the abovedescribed photosensitive and substantially light insensitive silverhalide emulsion in a total amount of silver halide corresponding to 2.24g of AgNO₃ /m² to a polyethylene terephthalate film support coated witha hydrophilic adhesion layer. The total amount of gelatin in this layerwas 2.21 g/m² and 10.7% of the total amount of AgNO₃ corresponded tophotosensitive silver halide. The layer further contained 0.7 mmol ofcompound 21A mentioned above.

A comparative imaging element was prepared similar to the abovedescribed imaging element with the exception however that compound 21Awas 1 eft out.

The thus obtained imaging elements were information-wise exposed andsubsequently developed during 1min, at room temperature in a developingliquid having the following composition and fixed using a fixingsolution containing thiosulphate (G333 commercially available fromAgfa-Gevaert N.V.).

Composition of developing liquid:

    ______________________________________                                        KBr                0.8       g/l                                              benzylalcohol      12        g/l                                              sodium carbonate   50        g/l                                              glycol             50        g/l                                              1-phenyl-3-pyrazolidone                                                                          0.25      g/l                                              p-phenylenediamine 7.5       g/l                                              sodium sulphite    5         g/l                                              uracil             2.24      g/l                                              sodium hydroxide   to adjust to pH = 11.5                                     ______________________________________                                    

The transmission density of the comparative imaging element was 0.08 inthe exposed areas and 0.06 in the non-exposed areas while the density ofthe imaging element according to the invention was 0.48 in the exposedareas and 0.06 in the non-exposed areas. Furthermore for the comparativeimaging element it was found that 7% and 1% of the total amount ofsilver halide was developed in respectively the exposed and non-exposedareas while the imaging element according to the invention showed thatrespectively 74% and 5% of the total amount of silver halide weredeveloped.

The present example thus shows that when a sensitizer releasing compoundaccording to the invention is used an image with good differentiationbetween exposed and non-exposed parts can be obtained without reversalof the image values.

EXAMPLE 6

An imaging element was prepared, exposed and processed as described inexample 5 with the exception however that compound 9A mentioned abovewas used instead of compound 21A. The amount of silver halide developedin the exposed and non-exposed areas was respectively 87% and 4%. Thedensity in the exposed and non-exposed areas was respectively 0.7 and0.06.

EXAMPLE 7

A photosensitive silver halide emulsion containing 2.7 mol % of AgBr and97.3 mol % of AgCl was prepared using the double jet method. The averagesize of the silver halide particles was 0.77 μm.

A substantially light insensitive silver chloride emulsion was preparedaccording to the double jet method. The average size of the silverchloride particles was 0.094 μm. The silver chloride particles weredoped with rhodium(III)chloride in an amount of 0.140 mmol per mol ofAgNO₃ to reduce their speed and stabilized with a phenylmercaptotetrazole derivative.

An imaging element was prepared by coating a mixture of thisphotosensitive and substantially light insensitive silver halideemulsion in a total amount of silver halide corresponding to 1.96 gAgNO₃ /m² to a polyethylene terephthalate film support coated with ahydrophilic adhesion layer. The total amount of binder (gelatin) in thislayer was 1.87 g/m². 18% of the total amount of AgNO₃ corresponded tophotosensitive silver halide. This layer further contained 0.6 mmol/m²of a hydroquinone and 0.4 mmol/m² of a 1-phenyl-3-pyrazolidone and0.6mmol/m² of compound 2A mentioned in table 5. To the thus obtainedelement was coated a layer of gelatin in an amount of 0.5 g/m².

The thus obtained imaging element was information-wise exposed andsubsequently developed with the following processing solution for 35 s:

    ______________________________________                                        sodium sulphite (anhydrous)                                                                            35     g/l                                           potassium bromide        0.82   g/l                                           hydroquinone monosulphonate                                                                            13     g/l                                           1-phenyl-3-pyrazolidone  4      g/l                                           sodium thiosulfate (anhydrous)                                                                         0.82   g/l                                           methylethanolamine       12     ml/l                                          sodium hydroxide         10     g/l                                           1-phenyl-5-mercaptotetrazole                                                                           0.15   g/l                                           3,4-dichloro-1-phenyl-5-mercaptotetrazole                                                              0.01   g/l                                           ______________________________________                                    

The imaging element was then processed for 30 s in an aqueous solutioncontaining 20% of acetic acid and finally fixated with a solutioncontaining 138 g/l of a thiosulphate.

The transmission density measured in the exposed areas of the imagingelement was 0.24 and 3.06 in the non-exposed areas.

We claim:
 1. A method for obtaining an image comprising the stepsof:information-wise exposing a photographic material comprising on asupport (i) photosensitive silver halide particles, (ii) substantiallylight insensitive silver salt particles having a speed at least a factor10 less than said photosensitive silver halide particles under the sameconditions of exposure and development of said photosensitive silverhalide particles and (iii) a releasing compound capable of image-wisereleasing under the conditions for image-wise development of saidphotosensitive silver halide to silver a chemical sensitizer, saidchemical sensitizer rendering said substantially light insensitivesilver salt particles developable developing said information-wiseexposed photographic material in an alkaline processing solution in thepresence of (a) developing agent(s) and containing (a) silver halidesolvent (s).
 2. A method according to claim 1 wherein said substantiallylight insensitive silver salt particles are silver halide particles. 3.A method according to claim 1 wherein said releasing compoundcorresponds to one of the following formulas (A) or (B):

    CAR--(TIME).sub.n --Q                                      (A)

wherein CAR represents a carrier moiety that upon reaction with eitherthe reduced or oxidized form of a developing agent or upon reaction withsilver ions is capable of releasing under the conditions for developmentof the photosensitive silver halide the moiety --(TIME)_(n) --Q, TIMErepresents timing group which releases Q subsequent to the release of--(TIME)_(n) --Q from CAR, Q represents a chemical sensitizer capable ofrendering silver salt particles developable and n represents 0 or 1;##STR60## wherein CAR has the same meaning as defined above, xrepresents an integer from 2 to 20, Y represents S, Se or Te, and Zrepresents the necessary atoms to form together with Y_(x) and CAR aring.
 4. A method according to claim 3 wherein Q of said formulacorresponds to one of the following moieties:

    --Y.sub.x --(TIME).sub.t --CAR'

wherein x and Y have the same meaning as defined in claim 3, t is 0 or 1and CAR' has one of the significance given for CAR defined in claim 3and may be the same as CAR but may also differ from CAR provided thatboth CAR and CAR' react in the same manner

    --Y.sub.x --R.sup.8

wherein x and Y have the same meaning as defined in claim 3 and R⁸represents an alkyl, alkylaryl, aryl or acyl group that may besubstituted;

    --S--SO.sub.2 R.sup.8

wherein R⁸ has the same meaning as defined above ##STR61## wherein eachof R⁹ and R¹⁰ independently represent hydrogen, an alkyl, aryl or acylgroup that may be substituted, L represents a divalent linking group##STR62## wherein L, R⁹ and R¹⁰ have the same meaning as defined above.5. A method according to claim 1 wherein said releasing compound iscapable of releasing under the conditions of development of saidphotosensitive silver halide to silver said chemical sensitizer uponcross-oxidation or cross-reduction with a developing agent.
 6. A methodaccording to claim 1 wherein said releasing compound is capable ofreleasing the chemical sensitizer under the conditions of development ofsaid photosensitive silver halide to silver upon a coupling reactionwith the oxidized form of a developing agent.
 7. A method according toclaim 1 wherein said photosensitive silver halide particles and saidsubstantially light insensitive silver salt particles are present in thesame layer.
 8. A method for obtaining an image according to theDTR-process comprising the steps of:information-wise exposing aphotographic material comprising on a support (i) photosensitive silverhalide particles, (ii) substantially light insensitive silver saltparticles having a speed at least a factor 10 less than saidphotosensitive silver halide particles under the same conditions ofexposure and development of said photosensitive silver halide particlesand (iii) a releasing compound capable of image-wise releasing under theconditions for image-wise development of said photosensitive silverhalide to silver a chemical sensitizer, said chemical sensitizerrendering said substantially light insensitive silver salt particlesdevelopable contacting said information-wise exposed photographicmaterial with an image-receiving material comprising on a support alayer containing physical development nuclei, developing saidinformation-wise exposed photographic material whilst in contact withsaid image-receiving material in an alkaline processing solution in thepresence of (a) developing agent(s) and containing (a) sirvet halidesolvent(s), separating said image-receiving material from saidphotographic material.
 9. A method according to claim 8 wherein saidsubstantially light insensitive silver salt particles are silver halideparticles.
 10. A method according to claim 8 wherein said releasingcompound corresponds to one of the following formulas (A) or (B):

    CAR--(TIME).sub.n --Q                                      (A)

wherein CAR represents a carrier moiety that upon reaction with eitherthe reduced or oxidized form of a developing agent or upon reaction withsilver ions is capable of releasing under the conditions for developmentof the photosensitive silver halide the moiety --(TIME)_(n) --Q, TIMErepresents timing group which releases Q subsequent to the release of--(TIME)_(n) --Q from CAR, Q represents a chemical sensitizer capable ofrendering silver salt particles developable and n represents 0 or 1;##STR63## wherein CAR has the same meaning as defined above, xrepresents an integer from 2 to 20, Y represents S, Se or Te, and Zrepresents the necessary atoms to form together with Y_(x) and CAR aring.
 11. A method according to claim 10 wherein Q of said formulacorresponds to one of the following moieties:

    --Y.sub.x --(TIME).sub.t --CAR'

wherein x and Y have the same meaning as defined in claim 10, t is 0 or1 and CAR' has one of the significance given for CAR defined in claim 10and may be the same as CAR but may also differ from CAR provided thatboth CAR and CAR react in the same manner

    --Y.sub.x --R.sup.8

wherein x and Y have the same meaning as defined in claim 10 and R⁸represents an alkyl, alkylaryl, aryl or acyl group that may besubstituted;

    --S--SO.sub.2 --R.sup.8

wherein R⁸ has the same meaning as defined above ##STR64## wherein eachof R⁹ and R¹⁰ independently represent hydrogen, an alkyl, aryl or acylgroup that may be substituted, L represents a divalent linking group##STR65## wherein L, R⁹ and R¹⁰ have the same meaning as defined above.12. A method according to claim 8 wherein said releasing compound iscapable of releasing under the conditions of development of saidphotosensitive silver halide to silver said chemical sensitizer uponcross-oxidation or cross-reduction with a developing agent.
 13. A methodaccording to claim 8 wherein said releasing compound is capable ofreleasing the chemical sensitizer under the conditions of development ofsaid photosensitive silver halide to silver upon a coupling reactionwith the oxidized form of a developing agent.
 14. A method according toclaim 8 wherein said photosensitive silver halide particles and saidsubstantially light insensitive silver salt particles are present in thesame layer.
 15. A method for obtaining an image according to theDTR-process comprising the steps of:information-wise exposing aphotographic material comprising on a support (i) photosensitive silverhalide particles, (ii) substantially light insensitive silver saltparticles having a speed at least a factor 10 less than saidphotosensitive silver halide particles under the same conditions ofexposure and development of said photosensitive silver halide particles,(iii) a releasing compound capable of image-wise releasing under theconditions for image-wise development of said photosensitive silverhalide to silver a chemical sensitizer, said chemical sensitizerrendering said substantially light insensitive silver salt particlesdevelopable and (iv) a layer of physical development nuclei anddeveloping said information-wise exposed photographic material in analkaline processing solution in the presence of (a) developing agent(s)and containing (a) silver halide solvent(s).
 16. A method according toclaim 8 wherein said support of said image-receiving material carries ahydrophilic surface.
 17. A method for preparing a lithographic printingplate according to the DTR-process comprising the stepsof:information-wise exposing a lithographic printing plate precursorcomprising on a support (i) a photosensitive silver halide, (ii) asubstantially light insensitive silver salt having a speed at least afactor 10 less than said photosensitive silver halide particles underthe same conditions of exposure and development of said photosensitivesilver halide particles and (iii) a releasing compound capable ofimage-wise releasing under the conditions for image-wise development ofsaid photosensitive silver halide to silver a chemical sensitizer, saidchemical sensitizer rendering said substantially light insensitivesilver salt particles developable and (iv) a layer of physicaldevelopment nuclei as an outermost layer on the photosensitive side ofsaid support, and developing said information-wise exposed photographicmaterial in an alkaline processing solution in the presence of (a)developing agent(s) and containing (a) silver halide solvent(s).
 18. Amethod for preparing a lithographic printing plate according to claim 17wherein the support of said photographic material is paper or apolyester film support.
 19. A method for preparing ,a lithographicprinting plate according to the DTR-process comprising the stepsof:information-wise exposing a lithographic printing plate precursorcomprising on a hydrophilic support provided with an image receivingsurface or image receiving layer containing physical development nuclei(i) a photosensitive silver halide, (ii) a substantially lightinsensitive silver salt having a speed at least a factor 10 less thansaid photosensitive silver halide particles under the same conditions ofexposure and development of said photosensitive silver halide particlesand (iii) a releasing compound capable of image-wise releasing under theconditions for image-wise development of said photosensitive silverhalide to silver a chemical sensitizer, said chemical sensitizerrendering said substantially light insensitive silver salt particlesdevelopable, developing said information-wise exposed photographicmaterial in an alkaline processing solution in the presence of (a)developing agent(s) and containing (a) silver halide solvent(s) toobtain a silver image on said image receiving surface or in said imagereceiving layer, and removing all layers above said silver image toexpose said silver image by means of rinsing with water.
 20. A methodaccording to claim 19 wherein said hydrophilic support is an aluminiumsupport.